The present invention relates generally to power transmission chains, and more particularly, to a power transmission chain system in which the chains are phased or offset by a portion of a pitch length or a portion of a sprocket tooth. The phasing of the chain and sprocket system modifies the noise characteristics of the system.
Power transmission chains are widely used in the automotive industry in automobile transmission systems as well as in engine timing drives. Engine timing systems conventionally include at least one driving sprocket located on the crankshaft and at least one driven sprocket located on a camshaft. Rotation of the crankshaft causes rotation of the camshaft through a chain and sprocket system. In automotive transmission systems, power transmission chains are used, for example, between a torque converter and the input to an automatic transmission. Power transmission chains are also used in transfer cases for four-wheel drive vehicles.
Noise is associated with chain drives. Noise is generated by a variety of sources, including the impact sound generated by the collision of the chain and the sprocket at the onset of meshing, and the chordal action of the chains and sprockets.
As to the impact sound generated, loudness is affected by, among other things, the impact velocity between the chain and the sprocket, and the mass of chain links contacting the sprocket at a particular moment or time increment. The meshing impact sound is generally a periodic sound in chain drives because the impact sound is repeated with a frequency generally equal to that of the frequency of the chain meshing with the sprocket. The frequency is related to the number of teeth on the sprocket and the speed of the sprocket. The impact can therefore produce sound having objectionable pure sonic tones.
Chordal action occurs as the chain link enters the sprocket from the free chain. The meshing of the chain and sprocket at the chain mesh frequency can cause a movement of the free chain or span (the part of the chain between the sprockets) in a direction perpendicular to the chain travel but in the same plane as the chain and sprockets. This vibratory movement can also produce an objectionable pure sonic tone at the frequency of the chain mesh frequency or a derivative thereof.
Many efforts have been made to decrease the noise level and pitch frequency distribution in chain drives so as to minimize the objectionable effects of the pure sonic tones. For example, U.S. Pat. No. 5,427,580, which is incorporated herein by reference, discloses the phasing of sprockets so as to modify the impact generated noise spectrum as well as the chordal action noise spectrum. The present invention utilizes the concepts taught in U.S. Pat. No. 5,427,580, in a sprocket system.
The phased chain system of the present invention includes phasing of two sprockets with respect to one another along a driving or driven shaft. Phasing of sprockets can reduce the number of chain link teeth (or mass of chain) impacting the sprockets along the shaft during a given time increment. Similarly, phasing the sprockets can alter or phase the chordal action or articulation of the chains and sprockets, and the resulting impact and chordal action generated noise.
Prior art chain drives have provided for the phasing of sprockets. However, in these chain drives, the two sprockets are machined on a single hub along the shaft. Such a system requires a complicated manufacturing process to machine two sprockets on a single hub.
Other prior art phased systems have used a pair of sprockets that are bolted together or riveted together to maintain the sprockets in the phased or offset positions. Such a system requires the manufacturing step of placement of the two sprockets in the offset position and then riveting or bolting in position.
In contrast, in its preferred embodiment, the present invention utilizes an sprocket assembly formed of separate, but identical pieces. Each of the sprockets have projections or grooves, such as splines or keyways, which are fitted to corresponding splines or keyways on a central shaft. Each sprocket can be assembled on the central shaft in at least two orientations, where each orientation results in a different alignment of the outer sprocket teeth. By positioning of one sprocket in one orientation, and other sprockets in other orientations, the phased or offset relationship can be attained. The sprocket assembly of the present invention provides advantages in the manufacture of sprockets and assembly.